var doc=fl.getDocumentDOM();
var tl=doc.getTimeline();
var layers=tl.layers;

for(var i=0;i<layers.length;i++){
	if(layers[i].layerType=="mask"){
		tl.setSelectedLayers(i,i);
		tl.setLayerProperty("locked",true,"selected");
		tl.setLayerProperty("visible",false,"selected");
	}
}